“Streaming” is a broad term for the delivery of time-ordered data such that the beginning will be consumed (e.g., fed into another system for display) before the end is completely delivered. The distinguishing characteristic of streaming is that the data contains desired consumption times relative to the consumption of the beginning of the stream. For example, a desired consumption time for video streaming may be of the following form: the millionth byte is used to generate the three-hundredth frame of a 30 frame per second video stream and thus should be received within 10 seconds of the consumption of the first byte.
Live streaming is streaming that is characterized by a relatively short delay between the instant at which data enters the transmitting unit and the instant at which the transmitted data is affected by this data. The content of a live stream may include audio, video, stock ticker data, database updates, telemetry, delta or change propagation data and many other types of data.
The term “live streaming” can apply to data that is not “live” in the common-language sense of being generated contemporaneously with the data communication. For example, it is clear that a system that sends digitized video of a sporting event to a receiver that displays the video with short delay is a live streaming system. But one may also apply live streaming techniques to a recorded movie; from the point of view of the streaming transmitter, the information from the movie playout device is a live stream.
A reliable live streaming system accurately reproduces at a one or more receiver the content of a live data stream that is present at a transmitter, most of the time, despite the loss of some of the transmitted data. The most common methods for reliable communication of non-streaming data on computer networks include the use of the TCP and IP protocols. The use of TCP/IP has significant disadvantages for live streaming, especially if a single transmitter is communicating with a large number of receivers. With TCP/IP, the sender is virtually connected to each receiver with an independent, variable-rate, reliable, byte-granularity channel. The variable-rate property is problematic for satisfying the delivery deadlines of live streaming, and the fact that each connection is independent means that some resources of the transmitter are consumed in linear proportion to the number of receivers. For these reasons, it is often preferable for the reliability mechanisms to be based on forward error correction (FEC) codes rather than retransmission of lost data.
A live streaming system has several important performance measures, including the loss protection, protection period, and startup time. Loss protection is defined as the fraction of the live stream data that can be lost over a specified period of time without interrupting the timely reconstruction of the live data stream at the receiver. The protection period is defined as the period of time over which the loss fraction is measured (the loss fraction may be higher for shorter periods of time). The startup time is generally defined as the time from the beginning of reception of data until the uninterrupted reconstruction of the live data stream can begin.
Unfortunately, current systems which employ FEC for live streaming are severely limited in the combinations of these performance measures that can be achieved, in the degree of variation in these performance measures that can be achieved during the reception of a live stream, and in the degree of variation in these performance measures for different receivers that are receiving the same live data stream. What is therefore needed is a system and method for communicating the content of a live data stream with improved parameters, such as high reliability, short startup time, and an extended protection period.